The invention relates to a motor vehicle with a high-voltage network and a high-voltage source, for example a traction battery. The invention also includes a method for controlling connecting the high-voltage source to the high-voltage network. The term high-voltage in the context of the present invention means an electric DC voltage of greater than 60 Volt, in particular greater than 200 Volt.
In motor vehicles, in particular electrically driven motor vehicles, it can be provided to supply electric consumers with high-voltage. For this purpose, the high-voltage consumers are coupled with a high-voltage source, for example a traction battery, a high-voltage generator with rectifier or a fuel-cell stack, via an intermediate circuit, for example busbars. The high-voltage consumers and the high-voltage intermediate circuit together form a high-voltage network, which is supplied with electric power by the high-voltage source. A high-voltage consumer can for example be an electric drive motor with inverter or an air conditioning system.
In such high-voltage vehicles, usually a pre-charging for charging the high-voltage intermediate circuit is performed in order to charge the intermediate-circuit capacitances that effectively receive power through the connection of the high-voltage source to the high-voltage network. Without this pre-charging the intermediate capacitance would suffer damage from the very high switch-on current. Likewise, the high-voltage switches of the high-voltage source would also suffer damage when being closed without pre-charging. After the start of the pre-charging, which is usually realized via a pre-charging relay and pre-charge resistor, the high-voltage generated by the high-voltage source is also reached in the high-voltage intermediate circuit after a predetermined time period. This pre-charging usually takes less than one second, i.e., for example a few 100 milliseconds. Usually, in the case of a voltage delta, i.e., in case of a voltage difference between the high-voltage of the high-voltage source and the voltage of the intermediate circuit, a second main switch, connected in parallel to the pre-charging relay and the pre-charge resistor, is already closed between the high-voltage source and the high-voltage network. The main switch can for example already be closed at a voltage delta of less than 10 Volts.
Because the pre-charging has to occur very quickly, a very small pre-charge resistor is used having a value that is uncritical for the components of the high voltage network. For a person, however, the pre-charge current that flows in this case is potentially hazardous. The reason for conducting the pre-charging as quickly as possible is that in the absence of errors the driver should not have to wait unnecessarily before the motor vehicle is operational. On the other hand, in the case of a defect in the high-voltage network, a person may come into contact with lines or devices of the high-voltage network. This is in particular the case in repair shops when the high-voltage network has to be checked, for example after an accident. In this case the relatively small pre-charge resistor offers no protection when the damaged high-voltage network is connected to the high-voltage source, for example to take the damaged motor vehicle on a test drive. A possible defect is for example that a non-mounted screw contact on a high-voltage component leaves a high-voltage line without insulation in the motor vehicle. A person touching these contacts during the pre-charging process may suffer a dangerous electric shock.
From DE 10 2008 012 418 A1 a high voltage system for a motor vehicle is known in which an intermediate circuit capacitor can be charged via a pre-charge resistor before a high-voltage battery is connected directly, i.e., without pre-charge resistor, to the high-voltage intermediate circuit. During the pre-charging the pre-charge current is monitored. When the pre-charge current is absent it is concluded that a contact of the high-voltage battery to the high-voltage network is missing and as a consequence the pre-charging is interrupted. A disadvantage of this system is that during this measurement a current may flow which, due to the small pre-charge resistor, is hazardous to a person.
From DE 10 2010 015 312 A1 a high-voltage system for a motor vehicle is known, which includes a diagnostic device with a measuring device for measuring a voltage course at an intermediate circuit capacitor. In particular during the discharging process of the intermediate circuit capacitor, the voltage course is measured and analyzed regarding whether a malfunction of the high-voltage system exists. Also in this system, electric currents occur in the high-voltage network during testing for malfunctions, which may be dangerous to a person's life.